The present invention relates to flow batteries and particularly to hybrid redox flow batteries. Flow batteries are electrochemical devices in which the chemical energy stored in electro-active materials is converted to electrical energy. The electro-active materials include those for the negative electrode reaction and those for the positive electrode reaction. In flow batteries, the electro-active materials are typically stored externally to the power-conversion device and are introduced into the power-conversion device when the device is operated.
Unlike traditional batteries, where active materials, electrolyte, and separator are stored within the casing of the electrochemical cell, redox flow batteries feature electrolytes which are stored in external tanks, and are pumped into the cell during each charge/discharge cycle. One feature of redox flow batteries is that the energy is stored in the soluble oxidized/reduced species which exist in the electrolyte, unlike traditional batteries, where energy is stored in the bulk electrode materials, and which are thus subjected to mechanical and thermal stresses during cycling, thereby contributing to reduced battery cycle life.
Some advantages of redox flow batteries may include: rapid response times, moderate cost, modularity, transportability, low maintenance, and flexible operation. Redox flow batteries may also be capable of extended cycle life, as systems with greater than 10,000 charge/discharge cycles have been reported. Hybrid flow batteries have an additional advantage over standard flow battery designs in that no ion-exchange membrane is required. Such membranes are very expensive. They also often require repair or maintenance which takes the battery offline. Thus, hybrid flow batteries without such ion-exchange membranes allow for cost savings and reduced down time for maintenance.